1. Field of the Invention:
The present invention relates generally to the field of automatic transmissions, and more specifically to a transmission wherein an input shaft is connected to planet gears surrounding a sun gear, the sun gear is connected to a pump and an output shaft is connected to a ring gear, such that gradually restricting the flow of fluid from the pump slows movement of the sun gear and thereby causes the planet gears to progressively transmit more of their torque to the ring gear, and thus to the output shaft.
2. Description of the Prior Art:
There are several transmissions in the prior art employing planetary gear arrangements. All have fundamental disadvantages such as reliance on clutches, an absence of reverse, park or overdrive modes, or substantial complexity.
DeLalio, U.S. Pat. No. 3,969,957, issued on July 20, 1976, discloses a vehicle transmission having reverse, low forward and high forward speed planetary gear sets, and a planetary clutch. Problems with DeLalio include disadvantages stemming from the use of a clutch, such as a jolt when shifting, heat and wasted power, and the need for relatively frequent clutch adjustment. Also, the pump assembly can be replaced only by removing the entire transmission from the vehicle. Finally, no overdrive mode is provided.
Schauer, U.S. Pat. No. 3,796,111, issued on Mar. 12, 1974, teaches a hydromechanical transmission combining torque from both mechanical and hydraulic paths. Clutches are engaged to enter low and high speed ranges. The disadvantages of a clutch are compounded for this invention, since more than one clutch is provided. No less important is that no provision is made for reverse operation or for locking into park.
Reed, U.S. Pat. No. 4,164,156, issued on Aug. 14, 1979, is directed to a multi-range concentric gear train requiring gear shifting. It includes a several planetary gear sets which are concentric about a common centerline to provide four speed ranges. Reed has the multiplied disadvantages of four clutches as well as substantial complexity and expense. And, once again, one must remove the transmission from the vehicle to replace the pump assembly.
A second patent, U.S. Pat. No. 4,183,264, issued to Reed on Jan. 15, 1980. This patent discloses an improvement to the multi-range transmission in the form of an overrunning clutch to preclude the undesired backward motion of an element under critical load conditions. This Reed design once again requires shifting and the use of multiple clutches. No reverse or overdrive operation is provided.
Mizuno, U.S. Pat. No. 4,368,653, issued on Jan. 18, 1983, teaches another variation of the hydromechanical transmission. Speed ratio detecting means are provided to detect lower and higher limits of a predetermined speed ratio, together with clutch control means. Again, there are the disadvantages of multiple clutches, combined with high complexity and no park mode.
Kita, U.S. Pat. No. 4,776,233, issued on Oct. 11, 1988, discloses a transmission having low and high speed modes and clutches for shifting from one to the other. Once again, there are the disadvantages of using a clutch, including a lurch during shifting, even if minimized, the generation of heat and the need for relatively frequent adjustment.
Finally, there is Koyama, U.S. Pat. No. 4,941,371, issued on July 17, 1990. Koyama teaches a hydraulic transmission with a clutch valve to reduce the jolt experienced in engaging its clutch. Thus Koyama has the disadvantages of a clutch, and also provides no reverse, overdrive or park modes.
It is thus an object of the present invention to provide a transmission which provides a continuously variable ratio of input to output angular speed without the use of a clutch or the need to otherwise change gears while moving in a forward or a reverse direction.
It is another object of the present invention to provide such a transmission which includes overdrive, reverse, and park modes.
It is another object of the present invention to eliminate the need for a clutch or torque converter to disengage the drive motor from the transmission, as required for present automotive transmissions.
It is still another object of the present invention to provide such a transmission which permits access to pump means for servicing or replacement without the need to remove the transmission from the vehicle.
It is finally an object of the present invention to provide such a transmission which is simple in design, reliable, and inexpensive.